A refrigerant is a substance used for its thermodynamic properties in common household appliances, such as refrigerators, freezers, and air conditioners. A refrigerant is capable of reversibly changing between a gas and a liquid and transferring heat during a heat cycle. Many refrigerants, such as R-12 and R-134a, are environmentally harmful substances. Under the Clean Air Act, it is illegal to vent refrigerants during any service, maintenance, repair or disposal of an appliance. Thus, refrigerants must be removed and captured properly during appliance disposal and/or recycling.